Method of producing planar, double-diffused semiconductor devices

ABSTRACT

Described is method of producing double-diffused semiconductor devices, preferably of germanium, having at least three zones of alternately different conductance. These zones are produced by indiffusion of dopants, into the semiconductor body in accordance with the steps of the planar technique. The process is characterized by applying at least two insulating layers, which resist the diffusion temperature, to the surface of the semiconductor body prior to the diffusion. The combination of said insulating layers is so selected that they show variable masking properties with respect to the substances to be indiffused and may be comprised of a SiO2 layer and a Si3N4 layer.

U Umted States Patent 1191 1111 3,753,805 Meer 1 Aug. 21, 1973 METHOD OFPRODUCING PLANAR, 3,537,921 11/1970 Boland 148/187 x DOUBLE DIFFUSEDSEMICONDUCTOR 3,510,369 5/1970 Ernick et ail. 148/175 DEVICES 3,331,7167/1967 Bloem et a1 148/187 X 3,342,650 9/1967 Sekiet a1. 148/187 [75]Inventor: Winfried Meer, Hohenbrunn, 3,388,000 6/1968 Waters et a1148/187 X Germany 3,432,920 3/1969 Rosenzweig 148/187 x 3,437,533 4/1969Dingwall 148/189X [73] Assignee: Siemens Aktiengesellschaft, Munich andBerlin Germany Primary ExaminerAl1en B. Curtis [22] Filed: 19, 1968Attorney-Curt M. Avery, Arthur E. Wilfond, Herbert L. Lerner and DanielJ. Tick [21] Appl. No.: 706,539

[57] ABSTRACT [30] Foreign Application Priority Data Described is methodof producing double-diffused Feb. 23, 1967 Germany 8108474 semimnducmrdevices, Preferably Semanium, ing at least three zones of alternatelydifferent conduc- [52 us. c1. 148/187 These zones are Predueed byihdiffusieh efdep' 511 1111. C1. H011 7/02 ems, the semieehdueler bodyin eeeerdehee with [58] Field of Search 148/187, 189, 190, the Steps efthe Planet teehhique- The Preeese is ehat- 148/175; 23/191; 29/578;317/235 465 acterized by applying at least two insulating layers, whichresist the diffusion temperature, to the surface of [56] ReferencesCited the semiconductor body prior to the diffusion. The UNITED STATESPATENTS combination of said insulating layers is so selected that theyshow variable masking properties with respect to 3:3 at a] thesubstances to be indiffused and may be comprised 3:477:886 11/1969Ehlenberger. 148/187 a layer and a layer" 3,438,873 4/1969 Schmidt29/578 X 3 Claims, 9 Drawing Figures 1 METHOD OFPRODUCING PLANAR,DOUBLE-DIFFUSED SEMICONDUCTOR DEVICES My invention relates to a methodof producing double-diffused semiconductor devices, preferably ofgermanium, having at least three zones of alternately dif ferentconductance. These zones are produced by indiffusing dopants, whichdetermine the conductivity type into the semiconductor body, inaccordance with steps used in planar technique.

It is known in the production of high frequency transistors,particularly those of germanium, to use gallium and zinc to produce ap-doped region for emitter diffusion in (pnp) transistors and basediffusion in (npn) transistors. However, these elements have thedisadvantage that they are insufficiently if at all, masked by a maskinglayer such as SiO which prior to the diffusion processes is precipitatedon the germanium semiconducting surface. Thus with the aforementionedelements, it is impossible to produce planar structures in germaniumsemiconductor bodies.

It is also known that a Si N layer possesses optimum masking properties,particularly for gallium. Therefore, in order to produce semiconductorcomponents by the planar technique, with gallium as a dopant, thesemiconductor surface must be sequentially provided with 3 SiO, cover ormask and with a Si, N, cover or mask with the required diffusion stepscarried out between the production of the individual cover layers. Forexample, in the production of the emitter region in pnp transistors, apartial separation of the cover ie necessary. Due to the plurality ofproduction steps, particularly when germanium is the base substance, thediffusion data is greatly changed mainly because of the subsequentprocess steps being conducted at high temperatures, resulting in aconsiderable impairment of the electrical parameters of the thusproduced semiconductor devices.

My invention has among its objects the simplification of themanufacturing process in the production of planar transistors,particularly germanium transistors, and the production of npn or pnpstructures in the best possible way by utilizing the masking propertiesof Si N, layers.

I achieve this end by prior to the diffusion steps, applying to thesurface of the semiconductor body at least two insulating layers whichremain stable at the diffusion temperatures utilized. The combination ofinsulating layers is so selected as to provide variable maskingproperties with respect to the indiffused materials.

A further development of this invention is to use a combination of SiO,and si N for the insulating layers by precipitating the SiO, layerfirst, followed by precipitating the si l' l layer.

The individual layers are precipitated by pyrolysis of the correspondingorganic compounds. For example, the SiO, layer is precipitated, througha pyrolysis of tetraethoxysilane, Si(OC,H,) at 600 700 C while the Si N,layer is precipitated through pyrolysis of trisdiethylaminosilane,Sil-I(N(C,H at approximately 500. C. The SiO, layer may also be formedthrough a reaction of tetrachlorosilane, SiCl,, with carbon dioxide,C0,, at 800C. The Si N layer may also be formed by pyrolysis of silane,Sill or silicochloroform, SiI-ICl inthe presence of ammonia, NH,, attemperatures from 4.003 to 500 C.

According to a particularly preferred embodiment example, the SiO layeris precipitated at a layer 0.15 p. thick and the Si;,N in a layer 0.05p. thick.

It is also within the framework of this invention to indiffuse thedopants, which determine the respective regions, into the semiconductorbody in a single method step. This simultaneous diffusion of n and pdopants largely eliminates changes in diffusion data which occur inknown methods, by the required subsequent processes conducted at hightemperatures.

Another advantage of my invention is that when several diffusion stepsare necessary, the production of a new diffusion mask between individualdiffusion processes as required by previous technique may be avoided.Furthermore, it is not necessary to produce the insulation layer whichis sometimes necessary following diffusion, and prior to the vapordeposition of the contacts.

One embodiment of the present invention is to cover or coat thesemiconductor with a layer of a foreign oxide and a foreign nitride. Forexample, germanium can be covered with a SiO layer and a Si N layer. Itis also possible in the same manner, to precipitate other layers withpartial masking properties or to use other semiconductors, e'.g. A'"B"compounds, as the base or substrate layer.

My method is the first to succeed in producing double-diffused planargermanium transistors by using gallium as the dopant, in a singlediffusion process. The present invention may also be used to advantagefor producing integrated circuits, containing planar germaniumtransistors.

Specific details of my invention can be seen from the embodimentexamples with reference to the drawing wherein FIGS. 1-5 show themanufacture of an npn doublediffused planar germanium transistor inaccordance with the present invention; and

FIGS. 6 to 9 disclose another embodiment for the production of a pnpdouble-diffused planar germanium transistor in accordance with thepresent invention.

FIG. I shows an n-conducting semiconductor crystal disc 1 of a germaniumwherein an approximately 0.15 p. thick SiOQ layer 2 is precipitatedthrough pyrolysis of tetraethyoxysilane, Si(OC,I-I at approximately700C. In FIG. 2 an approximately 0.05 1. thick Si N layer 3 is appliedto said SiO layer 2 by pyrolysis of trisdiethylaminosilane, SiH(N(C H at500 C. Another SiO layer 4 is applied upon the Si N, layer 3 as anetching mask for the Si N layer 3. A window 5 is etched into layers 3and 4 by the known photo resist method. As shown in FIG. 3, after theremaining photo resist is removed a p-doped region 6 using gallium asthe dopant is indiffused through window 5. The SiO layer 4 serves onlyas an etching mask for etching the base diffusion window 5 by aphosphoric acid solution at 180C into the Si N, layer 3, and maypossibly be substituted by a heat-resistant photo resist. As thediffusion is masked only by the remaining Si N, layer 3, it is notnecessary to remove the SiO, layer 2, lying beneath the Si;,N layer 3.FIG. 4 shows the production of the emitter region 7 by indifussion ofarsenic through window 8, etched into the SiO, layer 2 by the phototechnique using a dilute. hydrofluoric acid solution.

buffered by ammonium flouride. FIG. 5 shows the tinished transistorwhich was completed by etching an additional window into the SiO, layer2 for the base termina] and thereafter vapor depositing metal contacts 9and 10 through the remaining regions of insulation layer 2 and 3. Thecollector terminal is located on the bottom side of the semiconductorcrystal disc 1V and is not shown in the FIG. Otherwise, the referencenumerals are the same as used in FIG. 4.

FIG. b shows the two first production steps for the production of a pnpdouble-diffused planar transistor of germanium with one unmasked, andone masked, insulating layer. An unmasked layer 12, for example,crystalline SiO is precipitated, as described above, upon a p-conductingcrystal disc 11 of germanium. A masked insulation layer 13 is applied,for example si N is pyrolytically precipitated as described above, uponthe SiO, layer 12. By using the known photo resist method, and possiblyan SiO layer (not shown) as an etching mask, window 14 is etched intothe masking Si N layer 13 by a phosphoric acid solution at 180. Theemitter region 15 is produced by gallium indiffusion to give the deviceshown in FIG. 7. After providing a window 16 for the base region byremoving the Si -,N layer 13 and the SiO layer 12 thereat, the baseregion 17 is produced by indifussion of arsenic to provide the deviceshown in FIG. 8. In FIG. 9 the finished pnp double-diffused germaniumtransistor is shown after again producing SiO, layer 12 by oxidation andetching of contact terminal windows into the SiO layer 12, contact leadsl8 and 19 are vapor deposited through the remaining insulating layers 12and 13 to give the emitter and the base contacts, as described in FIG.5. The same numerals are used as in FIG. 8.

I claim:

1. The method of producing double-diffused germanium semiconductordevices, having at least three zones of alternately differentconductance types, produced by indifiusion of dopants, into thegermanium semiconductor body which comprises applying at least two ofthe insulating layers, which remain constant at the diffusiontemperature, to the surface of the germanium semiconductor body, thecombination of said insulating layers being an SiO layer and an Si Nlayer, said SiO layer is first precipitated in a layer thickness of 0.15and thereafter the Si N layer is precipitated, said insulating layersshowing variable masking properties with respect to the substances to beindiffused and thereafter indiffusing the dopants through a window inthe Si N layer and through the SiO layer.

2. The method of claim 1, wherein the si N layer is applied to athickness of 0.05 p.

3. The method of claim 1, wherein the indiffusion into the semiconductorbody of the dopant determining the respective zones is effected in asingle method step. =0

2. The method of claim 1, wherein the Si3N4 layer is applied to athickness of 0.05 Mu .
 3. The method of claim 1, wherein the indiffusioninto the semiconductor body of the dopant determining the respectivezones is effected in a single method step.